Heroes of Olympus and the Lyoko Warriors
by Reincarnations
Summary: The war with Gaea is over and the immortal children of Zeus decided that a certain demigod deserves a gift, finding their older brother. Who better to find him than the famous Percy Jackson and Annabeth Chase? With the help of the Lyoko Warriors, they find the brother and who his mysterious sibling is.
1. Chapter 1

**_Okay, this story idea came up out of the blew when I thought of Percy and Annabeth going to Lyoko. Then I thought, "What if they encounter William when he's possessed?" Then I kept getting more and more ideas so I'm writing it! I know there is only twelvish stories in the cross-over categories but someone might read it and actually like it._**

 ** _Disclaimer for ALL chapters so I don't repeat myself: I do not own the PJO/HOO series or Code Lyoko._**

 ** _Enjoy._**

* * *

Though the war with the giants had come to an end, there was still something that needed to be taken care of. Something that two specific demigods would have to handle.

"So we have to do what exactly?" Percy asked his old teacher for clarification.

Chiron explained as best as he could. "You and Annabeth have to go to France and save a demigod."

Annabeth inquired, "What happened to him?"

"He disappeared," Chiron adverted his gaze to Percy. "Much like you did, except almost no one knows who he is. All I know is he's Roman and he's important to a camper at Camp Jupiter."

"Who?"

"I can't give you the details," he acknowledged. "The immortals, mainly the children of Zeus, are the ones who are assigning you two the quest. You are to attend a school known as Kadic Academy and befriend a group of students. These students should be able to help you find him or, at least, that's what I'm told.

"Luckily, your late admissions in the school was easy because the principal has a daughter who is a demigod. She managed to bargain with him."

The couple exchanged a questioning look but Percy asked, "Who is she?"

"Me." The two turned around to find it was Drew that spoke. With an annoyed sigh she explained while Chiron walked away, "My father had divorced his wife when I was about five or six. I went with her instead of him. She remarried and I never spoke to my father again. The only reason I was able to convince him is if I'd come visit him."

"Just a little heads up," Drew continue, "he knows about the immortals because he can see through the Mist, so he will excuse any 'misconduct' as he put it. I did try to have you two stay in the same room, since I knew you were sleeping in the same cabin here, but he wouldn't budge. He argued that he is already paying for your tuition so he doesn't need you breaking the rules on the first day."

"Thank you for trying." Annabeth thanked after a moments hesitation. "You've changed a lot since the war started, and that's good."

Drew offered a small smile, but then she remembered something. "Oh! I have a half-sister on my father's side that's also attending the school, she should be in the freshman class. Her name is Elizabeth, but she gave herself a stupid nickname."

"Which is?"

"Sissi."

* * *

"How's the depossessing process for William going?" Yumi interrogated Jeremie as she sat down at their usual table at lunch.

"It would go better if I knew where he is on Lyoko." Jeremie confessed with a sigh. "I need a sample of his genetic structure so I know what it is that's making Xana posses him."

"You need to hurry it up." Ulrich advised in a whisper so no one could over-hear them. "After the clone disappeared, everyone thought he left school to stay with his parents, but then they call demanding to know where he is."

"I know, I know." Jeremie repeated in a hurry. "I'm going as fast as I can but the four of you need to-"

"Hey!" Aelita called from the other side of the cafeteria as she ran over to her friends. Panting slightly, she asked, "Did you hear about the new students?"

"New students?"

"Odd is showing them around right now." Aelita stated as she sat next to Jeremie. "They're from a place called Manhattan. I think they should join our group."

"We don't know their names Aelita." Yumi argued. "You know what happened last time we let someone join and why do you think they should?"

"Because the boy made the comment about the girl being a super genius. She can figure out anything and everything about how to work a computer. If you, me and Jeremie weren't there to work the supercomputer, she can do it. Besides, if she's not needed to do that they can still fight in Lyoko.

"They talked about how they went to this summer camp. They learned archery, climbing skills, and how to fight too. They fit the spot perfectly!"

"But-"

"Hey guys!" The group turned to see Odd walking their way with two students who appeared to be a year older than Yumi. The boy had dark black hair and sea green eyes that appeared to glow. The girl beside him was a couple inches shorter than him with blonde hair that was in a pony tail and grey stormy eyes. The group immediately noticed the tattoo on the guy's arm, how they were wearing matching necklaces, and the exposed scars on their skins.

Odd came up to the group with his normal goofy smile on his face carrying his lunch tray. He sat next to Ulrich as he said, "Meet the new students. He's Percy Jackson and she's Annabeth Chase. They came all the way from New York!"

"Hi," Annabeth said almost shyly, "Do you mind if we sit here? Odd and Aelita are the only students we know."

Without a moments hesitation, the group scooted over for their new friends. Noticing the two didn't have a tray, Ulrich asked, "You're not hungry?"

Percy shook his head. "I took her out for lunch before we arrived."

"So you two are. . .?"

"We're dating," Annabeth finished as Percy wrapped an arm around her waist. "We've been together so long that we can basically read each other's mind."

The bell ringed cutting off the group's conversation. "Are you doing anything after school?" Aelita asked the couple. When they answered no she continued, "We're going to show you where we go after school to hang out then. Trust me, you'll love it."

* * *

There was a slight _problem_ when the couple went to their class. They were having trouble reading the board when the teacher called on Percy. Percy begrudgingly explained that they both have dyslexia, though his was far worse than Annabeth's. At the revelation the teacher insisted that they go to a 'special' class to get some help. Annabeth, having been offended, refused and Percy agreed with her.

So there were the two, waiting for a 'parental figure' to talk with the principal. After what felt like forever, a parental figure did show up, but not one they were expecting. Walking into the waiting room, wearing casual yet formal clothing, was none other than Poseidon, the king of the seas. He gave his son a knowing wink before walking into the principal's office.

A couple incoherent yelling hours later, Mr. Delmas walked out with his cheeks red from the arguing. He gestured to the office when he told Percy, "Your father would like to speak to the both of you. Once he's finished, I'll have Mr. Della Robbia come and escort you to your shared room on the boy's floor. You are very lucky your father managed to convince me."

Mr. Delmas left while the two entered the office. Percy's father was sitting on the desk as he stared at the paintings on the wall. Noticing that they had arrived, Poseidon adverted his attention to them, "I didn't come here to settle the dispute about the class and living arrangements. I came to give you more details about your quest."

"First off the girl you met when you arrived, I believe her name is Aelita, she was turned into a digital program when she was young," he informed importantly. "She had been stuck in a virtual world for about ten years before someone discovered the virtual world. The friends she has now figured out a way to save her."

"Since the world was discovered the group of friends have been fighting inside the world to stop the virus inside from destroying the world. No one except them and the gods remember it because they can go back to the past before the attack started. You are to help them until you find and save the missing demigod."

"Can you give us any details about this demigod?" Percy asked his father. "It might help us."

"I'm afraid I can't." Poseidon denied. "The only reason I'm the one giving you the information is because Zeus's godly children doesn't want him to know about the quest. They want this demigod saved to thank the one that saved their sibling. Since Athena and I have agreed to a peace treaty, I volunteered to tell so he wouldn't get suspicious. Although I was told you were given permission to tell the group about the gods if you think it will help you on your quest."

"So we don't get a name?" Annabeth inquired on.

"No, but I was asked to give you some advice that you need to remember for the future." Poseidon leaned forward as though he was to tell a secret. "Don't be afraid to ask for help."

* * *

 ** _I'm just gonna end the chapter there. I've decided that I'm only going to add chapters if someone requests it. It would be a waste of my time to continue the story if no one is actually reading it._**

 ** _Anyways, thank you for reading and please review!_**


	2. Chapter 2

"So why did you two decide to come to Kadic?" Odd asked, casually leaned against the door as he watched the couple look around their room. "I mean, it's already a handful of months into the term and next month we get out a couple weeks for winter break."

Percy and Annabeth look at each other and when Annabeth nodded in permission, Percy told him, "We're looking for someone. We were told we'd be able to find him here."

"Who told you that?"

Another look prompted Percy to ask him, "What would you say if I told you it was the gods of Olympus and Annabeth and I are demigods?"

Though that was the strangest thing he ever heard, Odd replied almost like a challenge, "I would tell you to prove it."

Without a moments notice, Percy flicked his wrist at the water bottle in Odd's hand. The cap was twisted off and lifted from the bottle as the water rose out of it. The water floated around the room till it was above his head. The water spelled the sentence, 'I am the son of the sea god'.

Odd watched the water return to the bottle before he stated, "My mom used to tell me stories about the gods when I was a kid. Neptune is the sea god, right?"

"For us, it's Poseidon." Percy said, hiding that he was surprised that Odd wasn't. "Neptune is the Roman name while Poseidon is the Greek. Since you said Neptune you must be a Roman."

"There are different names?"

"There are different personalities." Annabeth corrected as she sat on the bed moved against the wall. "Like for my mother, Athena. As her Greek form, she has many children because she thinks them up. As for her Roman form, Minerva, she has no children because if a maiden were to have a children-"

"They would be killed," Odd interrupted/finished. "I remember asking my mom about- wait, aren't your parents enemies?"

"They were," Percy agreed, but Annabeth continued as she hugged him from behind, having to look past him to look at Odd, "But that was before hearing about their children falling into hell, surviving, and then going to the place where they became rivals to have their children confess their love for each other before they invaded the Giants' den."

Deciding not to ask them any questions about that, Odd asked a different one, "So there are more demigods?"

"Yes, there are two camps. The Roman camp, Camp Jupiter, is located in San Francisco, California. The Greek camp I've been at since I was seven, Camp Half-Blood, is located on Long Island South. We have a peace treaty so sometimes during school breaks, campers go to the opposite camp to see what it's like."

"That sounds like fun!" Odd exclaimed joyfully. "Can my friends and I visit one?"

The couple shared another look before Percy answered, "We will have to check with the ones in charge of the camp. They typically don't like-"

 _RING! RING!_

Odd grabbed his phone from his pocket and rolled his eyes at the caller I.D. "Jeremie's having one of his fits." Putting the phone on silence, Odd announced, "Well, since you told me your secret I guess I can tell you mine and my friends'."

"You don't-"

"Yep! On our way to the factory, I'm going to tell you all about Lyoko!"

* * *

"I can't believe you told them!" Jeremie exclaimed as he hurriedly typed away on the keyboard. When an alarm started to go off signalling that someone had low health and was close to being devirtualized. "Ugh, we don't have time for this! Head to the scanner room. I'll guide you two the best I can from here. Before you go remember this, don't fall off the edge because you will fall into the digital sea. When you touch the digital sea, you will be devirtualized forever, meaning you can't return to Earth, and none of us will be able to save you."

Another sound went off to notify that Yumi had be devirtualized. "Hurry!"

Before the romantic couple knew it, they were on the virtual world that Odd talked so well about in the ice region. They appeared as they would if they were in ancient Greek except they had no armor. All they had was a belt that had their weapons attached to it. When they fell from the sky and landed on their feet, Odd let out a short laugh. "You two are now the second and third person to actually land on their feet when being virtualized."

" _This is no time to joke around Odd!_ " Jeremie's voice called from the sky as they made the short run to Alieta and Ulrich. " _William is attacking them and Ulrich has only ten life points left_!"

They made it to the duo right when Jeremie finished his announcement. Ulrich deflected the attack and the made the mistake of turning his back. Before he could finish asking, "Why did you bring them here?", he was stabbed in the back and devirtualized by William.

"You two do know how to fight, right?" Odd asked after they rushed for cover by Alieta's side.

"We would be dead if we didn't." Percy retorted.

Aelita gave him a strange look but wasn't able to voice her thought because Odd already started speaking, "I'll lead Aelita to the tower while you two distract William. Whatever you do, don't get close enough to where he can hit you. If he hits you, you lose life points and when you lose life points you get devirtualized like Yumi and Ulrich di-"

Odd couldn't finish his statement because he got hit by a Megatank. "Change of plans," Annabeth quickly decided as Percy shot a stream of ice at the monster's eye, effectively killing it without looking at it. "Percy, you go with Aelita to the tower while I distract him. I'll make sure he doesn't come after you."

"Good luck," he encouraged as he led the way to tower with Aelita trying to run fast enough to catch up.

Annabeth turned herself to where she thought the enemy was, but he wasn't there. Scouring the area cautiously, she bumped into something behind. That something turned out to be William. He grabbed her arm tightly and when she raised her other arm that had her weapon, William knocked it out of her hand and gripped her wrist.

What appeared to be with all the strength he held, William stuttered out forcefully, "Ra...ra."

A sense of urgency flooded over her for an unknown reason as she asked, while struggling to get out of his grip, "What?"

"Ra...ra!"

Meanwhile Percy managed to get Aelita safely to the tower. After she entered the tower, Percy changed his attention to his girlfriend, who was far away and being held captive by the enemy.

 **Don't get devirtualized by the enemy,** a cautious voice in his head stated. **If you do, you'll return to Earth with those injuries and will need medical attention immediately.**

"Jeremie!" Percy yelled at the sky as he ran for his girlfriend. "Materialize Annabeth!"

" _Why?"_ His voice echoed in the sky. _"There's no point for me to do so. She only has ten life points left anyways."_

"I swear, if you don't do it right now, I'll-"

Percy stopped himself from talking and moving as he watched his girlfriend disappear from thin air. Anger enveloped himself as he raised his arm level with William, who had turned himself around to look at him. He raised his hand high above his head with part of the digital sea rising into the sky above William. He slammed his arm down with the sea following the movement, crashing down on William. Once it did, Percy came to his senses and forced the sea away from the enemy to see he had vanished.

"Jeremie!" Percy yelled to the sky as Aelita, who was running to him after deactivating the tower, stopped at his side. "What did I do? Did I kill him?"

 _"No."_ Jeremie reassured. " _He teleported himself to another sector before the sea could touch him, but how were you able to control of it?"_

"Odd can explain it to all of you later." Percy promised. "Just get us out of here."

* * *

After Jeremie devirtualized Percy and Aelita and after the came out of the scanners, Percy noticed Annabeth lying unconscious on the ground with shallow breathing. Instead of taking her to the the computer room where the others were at, he rushed out of the factory and ran as fast as he could to the school with her in his arms. The nurse checked her out and said her injuries weren't dire. According to her, Annabeth was knocked unconscious and should wake up in a handful of minutes.

After the nurse left the room, Annabeth, with her eyes still closed, muttered, "Is she gone?"

"Yes," Percy answered as he brought out a pastry from his pocket, "and I got you some ambrosia from our room. I got in-trouble by the P.E teacher though. Apparently we aren't allowed in the dorms until a certain time."

Annabeth opened her eyes and gladly took a bite out of the food he presented at her mouth. After she swallowed, she sat herself up while Percy asked, "So this William is the demigod we are supposed to save? How?"

"I think I have an idea," she confessed while her head started to throb. "When he grabbed me, he kept repeating the same thing over and over again; 'RARA'."

Something clicked inside Percy's head once she said that. "Dad wasn't talking about asking them for help, he was talking about-!"

"Do you think we can get her here?"

Percy stood from his chair and headed to the door. "I'll contact her then explain to the principle that we need her to complete the mission. I'll come back after I do, but until then you need to get some rest. I have a feeling we will have to fight a whole lot harder."

* * *

 ** _So I changed my mind because I saw someone had favorited the story. I'm going to add chapters whenever I get the time to complete them, like now for instance._**

 ** _Think you know who this RARA is? Of course you do; it's a joke in the PJO fandom._**

 ** _Please review!_**


	3. Chapter 3

"Guys!" Odd yelled as he caught up to his group of his friends that didn't contain Yumi. "I had a strange dream about this girl last night! She was amazingly beautiful, tall, long dark hair, dark eyes and-"

"Wearing a purple shirt that says 'Camp Jupiter'?" Ulrich guessed.

"How did you know?"

His friend pointed to the girl that was being escorted by the principal. She was exactly as Odd had described her, but he didn't state that she was carrying luggage. "That's Reyna." Annabeth provided as she moved away from her boyfriend's touch. "We asked her to come to Kadic to help us with our mission."

"RARA!" Percy shouted, which caught the attention of the two people, one who was staring at him curiously while the other was glaring at him. She dropped her bags onto the ground and walked to Percy. Once she was within arm length, Annabeth moved farther away as the others watch Reyna knock Percy onto the ground with her knee on his back and her hand pushing his head down on the ground.

"I _hate_ that nickname," Reyna practically growled into his ear. "Why would you call me that?"

"To get a rise out of you," Percy teased as he used strength to push himself off the ground, knocking Reyna off in the process. When the two stood to full height, Mr. Delmas came over.

"It seems like you two already know each other," he acknowledged. He turned his attention to Odd when he said, "Mr. Della Robbia, since you are still being punished for your unwillingness to participate in class, you will escort Miss Dunbar to her brother's room and then to her class. I will notify your teacher that you'll be a few minutes late for class."

Odd snapped out of his trance in time to say, "Yes sir."

That was when Reyna finally looked at him as Mr. Delmas walked away. She smiled kindly before outstretching her hand to her guide. "Don't worry, I only flipped him because he used my brother's nickname for me. I'm Reyna Dunbar."

"Dunbar?" Aelita asked as Odd shook Reyna's hand, though he was still in a trance by her beauty. "So you are William's younger sister?"

Reyna hesitated, but with a sigh answered, "I'm his younger _twin_ sister."

* * *

"Class," the foreign language teacher began, "let's welcome our new student, Reyna. . ."

"Dunbar," Reyna finished for the teacher didn't know her last name. "I'm Reyna Dunbar."

Yumi spoke out of turn when she impulsively asked, "So you're related to William?"

With another sigh, Reyna explained, "We are siblings. He's my older twin, but you already know that." Before Yumi could deny it, Reyna pulled out a locket that was tucked underneath her shirt. The locket had a carving of a girl and her Pegasus. "William wrote in his letter that you took the picture he put in here. He told me all about you and your friends, including a place called Lyoko?"

"Miss Dunbar, please take your seat and we will begin."

Reyna gracefully sat at the empty seat next to Yumi, not knowing it once belonged to her brother. Yumi leaned close to her and whispered as quietly as she could so the teacher wouldn't hear her, "How could he have written to you so quickly? He went missing the afternoon after."

Reyna turned her head and her eyes seemed to glow. "Don't underestimate the gods."

* * *

"Reyna, why didn't you tell anyone about William?" Annabeth asked the Roman warrior.

"I thought he was dead." She bluntly put it as she stabbed her lunch food, not really in the mood to eat. "He ran away from home when we were six because our dad was starting to go crazy. He wanted me to come with him, but I didn't because I wanted to stay with Hylla. Years passed and the day that Jason disappeared, Mercury delivered a letter to me. It was from William, who wasn't sure if I'd get the letter or not.

"You know, that was the only time when anyone would see Mercury, when he was delivering letters to me from my brother." Reyna commented, but then continued on with her explanation. "Anyways, when I had to take the Parthenon back to Camp Half Blood with Nico and Hedge, Mercury showed up the day after we were at my home town. He gave me the letter that William wrote me. 'Be careful out there RARA,' the letter had said. 'I don't want you to die before we meet again.'"

Reyna shook her head to get rid of a thought. "The day after the war ended, Lady Diana gave me a phone and said it was a gift for saving her hunters. The phone started to ring and she told me to answer. When I did, I heard someone say, 'Hey, RARA.' I fell to the ground and began to cry out of pure happiness. It was my brother, William.

"He told me, while he was crying too, that Mercury gave him a phone because he was his favorite customer. William explained the rule Mercury told him; we can only talk for one hour per week before the monsters start to track. Because of that we came up with a time schedule, ten minutes a day and on the seventh day we write each other."

Reyna laughed as she remembered something. "The day after I was telling him about what happened during the war. He was silent for a couple minutes until he finally snapped out of it and apologized. He was still trying to get over the fact that we were talking out of our letters."

"Wait," Ulrich requested. "You keep on saying he calls you 'RARA', I thought you hate that nickname?"

"I hate when other people call me that," Reyna corrected as she pushed her tray away from her. "When we were kids, William called me 'RARA' because he hated my name. He thought it meant that I was going to eventually leave him so he started calling me by that nickname."

The bell ringed which once again stopped the group's conversation. "After school we'll take you to Lyoko." Aelita promised as they stood from the table. "Trust me, you'll love it."

* * *

"Alright!" Odd exclaimed as the seven of them were virtualized in the desert region. "Welcome to Lyo-" Odd stopped himself after he turned to look at Reyna. Once again, he was at a loss for words. Reyna was dressed as if she was some sort of Roman princess, except she a cape like object attached to the top of her shoulder.

Reyna blushed slightly, wondering what was wrong with her. Luckily, Annabeth made a comment before anything could get awkward. "I guess this place taps into our fighting experience." She motioned to their demigod weapons. "We didn't have these when we came here but now we do."

Reyna held out her cape as she looked at it. "Do you think these copies have the same ability?"

" _You will find out in a second,"_ Jeremie's voice insisted from the sky. " _There is a swarm_ _of Kankrelats, Hornets, and Bloks coming your way. Aelita, Yumi, Ulrich, and Odd will only provide backup if the three of you need it. You need practice in fighting-"_

"So you're saying we are weak?" Reyna naturally assumed as she watched the strange looking monsters from a distance scurry closer to them.

Annabeth once again butted in. "That's not what he meant-"

 _"That's exactly what I meant."_ Jeremie argued, not helping the situation. _"The three of you don't have enough experience to fight in this world."_

Reyna glared at the direction of the monsters as she gripped her sword tightly. "You need to brush up on your Roman and Greek mythology." With that said, Reyna ran towards the ones who wanted to kill her with Annabeth and Percy quickly following her.

Odd sighed. "She's the preator of New Rome, meaning she is in charge and has the highest fighting skill. You saying she doesn't have experience is like you're challenging her position."

His three friends gave him a strange look. "How do you know that?" Ulrich asked.

"No reason. Now let's go fight these freaks."

* * *

 **Done! I hope whoever is reading this enjoyed it. Please review if you don't mind.**


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